1. Field of the Invention
The present invention relates to systems and methods for treating liquids and, more particularly, to systems and methods for pasteurizing citrus juice.
2. Description of Related Art It has been known since the days of Pasteur that, in order to prevent contamination over time by harmful microorganisms, liquids can be heat treated. In addition, in fruit juices, the enzyme pectin methylesterase (PME) causes a loss of quality in the product during storage. Commercial steam pasteurization is typically performed by passing the product through a metal heat exchanger; however, degradation of the juice can occur if care is not taken to minimize the temperature differential between the metal walls of the heat exchanger and the center of the liquid.
Various systems and methods of achieving pasteurization have been disclosed, including those of Huzenlaub (U.S. Pat. No. 2,517,569) and Gray (U.S. Pat. No. 3,092,503), who teach the utilization of infrared heating for sterilization. Similarly, electromagnetic waves may be used to heat a liquid, as discussed by Shaw (U.S. Pat. No. 2,585,970), who teaches the use of waves of frequency 500-5000 MHz to excite a conductive cavity through which fluid is directed.
Microwave heating has also been proposed to inactivate enzymes and microorganisms in fruit juices by Copson (U.S. Pat. No. 2,833,657) and by Le Viet (U.S. Pat. No. 4,694,133). In the latter of these, a swirling of the liquid is induced to achieve more uniform heating. The use of microwave energy avoids some of the problems associated with heating to high temperatures, including loss of flavor. This is due in part to the fact that the radiant energy heats the juice directly without heating the chamber walls, thus avoiding heat-transfer films and permitting improved temperature control. In addition, less heat is lost to the environment, and rapid startup and shutdown are possible.